In the packaging industry, use is often made of packaging containers of single-use disposable type for transporting liquid foods such as, for example, milk and juice, and a very large group of these so-called single-use packages is produced from a packaging laminate consisting of a core layer of paper or paperboard and outer, liquid-tight coatings of plastic, usually polyethylene, on both sides of the core layer. A conventional single-use package for, for example milk, is often produced from a packaging laminate which has a rigid, but foldable core layer of paper or paperboard and outer, liquid-tight coatings of plastic, preferably polyethylene, on both sides of the core layer. Such a single-use package has sufficient mechanical strength and stability to withstand external stresses to which the packaging container is exposed during normal transport and handling, at the same time as being sufficiently liquid-tight to efficiently prevent the packed liquid food from penetrating into the liquid-sensitive paper or paperboard layer.
A single-use package produced from a packaging laminate which only consists of paper or paperboard and outer, liquid-tight coatings of polyethylene as the single-use package described above has, however, no—or but insignificant—tightness properties against gases and cannot, therefore, be employed for packaging, for example, juice and cooking oil which are very rapidly broken down and destroyed in contact with oxygen gas. In order to impart to the single-use package sufficient tightness properties against gases, in particular oxygen gas, so that oxygen gas-sensitive products may also be packed and stored in it, the conventional packaging laminate is supplemented with at least one additional material layer possessing the requisite gas barrier properties.
Examples of such materials may be both organic materials and inorganic materials, but are normally an aluminium foil (Alifoil) between the core layer and the outer, liquid-tight plastic coating on the inside of the single-use package. An aluminium foil is practically entirely gas-tight and, in addition, enjoys the major advantage over, for instance, other organic barrier polymers, for example hydrolysed ethylene vinyl acetate copolymer (so-called EVOH), that it makes for simple, but rapid and efficient thermosealing of the packaging laminate by induction thermosealing. As was mentioned above, there has long been in existence a very large and constantly growing number of commercial single-use packages of varying sizes and shapes for liquid foods. A very well known example is the parallelepipedic single-use package which is sold under the trademark Tetra Brik® and which is most often employed for liquid foods of the type such as milk, juice etc. A Tetra Brik® package has a tubular container body of rectangular cross section and united, substantially planar end closures with four double-walled, triangular corner flaps folded down and fixedly sealed against adjacent outer walls on the outside of the package. Another well-known example of a commercial single-use package for liquid foods is the single-use package sold under the trademark Tetra Rex®. This package has a tubular container body of square cross section and a substantially planar bottom closure and gable-top closure in one piece with the tubular container body. Yet a further example of a well-known commercial single-use package for liquid foods is the package which is sold under the trademark Tetra Top® and which, like both of the previously mentioned single-use packages, has a tubular container body and a substantially planar bottom closure in one piece with the tubular container body. A Tetra Top® package differs from the two previously mentioned packages principally in that the tubular container body is of substantially circular cross section and that the top closure of the package consists of an injection moulded plastic lid with a peripheral, annular downwardly directed flange by means of which the plastic lid is fixedly sealed in liquid-tight fashion to the inside of the tubular container body.
Single-use packages of the types described above are most generally produced using modem filling machines which, from a web or from prefabricated blanks of a packaging laminate, form, fill and seal finished consumer packages in accordance with the so-called form/fill/seal technology.
From a sheet or web-shaped packaging laminate consisting of a core layer of paper or paperboard and outer, liquid-tight coatings of plastic, preferably polyethylene, mechanically strong and dimensionally stable single-use packages are thus produced with requisite physical tightness properties vis-à-vis both liquids and gases, in particular oxygen gas, in order to make for reliable transport and storage of the packed liquid food.
While the above-described, known packaging laminate consisting of a core layer of paper or paperboard and outer, liquid-tight coatings of plastic, preferably polyethylene, makes for reliable transport and storage of the packed food, it occasionally happens that problems may arise when the package, on being emptied, is grasped and lifted with one hand gripping around at least a part of the tubular container body of the package. More precisely, it has proved that the gripping force to which the package is subjected when it is grasped and lifted on being emptied occasionally needs to be so great that it is even greater than the mechanical gripping rigidity of the package, whereby the package, under the action of the applied gripping force, tends to buckle inwards into the package, with consequential accidental pouring and spilling of the contents, because of the reduction in volume caused thereby.
The problem with unintentional spilling on the emptying of the package may be perceived as more or less troublesome and irritating for the consumer, but becomes more manifest the greater the packed liquid volume is, since a package containing a large liquid volume is heavier than a package containing a slight liquid volume and therefore requires a correspondingly greater manual gripping force in order to be capable of being lifted when the contents of the package are poured out. The problem is also partly linked to the geometric configuration of the package and its dimensions, and may be particularly manifest if the package has a tubular container body with very large ratio between the length of the container body and the diameter of the container body or smallest cross-sectional dimension. However, this problem may be particularly troublesome and irritating in connection with a single-use package which has a tubular container body without vertical, rigidifying folding-or corner edges which extend all the way between the bottom and top closures of the package.
An earlier attempt to solve the above-described problem in connection with the conventional single-use packages has taken as its point of departure to increase the rigidity of the packaging laminate by increasing the thickness of the paper or paperboard layer employed. A paper or paperboard layer with increased thickness however makes the packaging laminate excessively thick and thereby unnecessarily difficult to fold-form, in particular in the regions where overlapping material layers are to be folded double, as is almost always the case when the packaging laminate is reformed into finished single-use packages. Moreover, the material cost for paper or paperboard is extremely high, and an increased paper or paperboard thickness would thus entail a relatively steeply increased material cost for the packaging laminate.
Another earlier attempt to solve the above-described problem has further taken as its point of departure to increase the rigidity of the packaging laminate with the aid of an additional layer of an aluminium foil on the one side of the paper or paperboard web, but this solution also entails steeply increased costs for the packaging laminate because of the extremely high manufacturing and material costs of the aluminium foil. Furthermore, an aluminium foil has a very low level of ductility and stretching and, as a result, cracks very easily when exposed to powerful tensile and flexural stresses, which occur during the reforming of the packaging laminate into packages, in particular in areas where overlapping parts of the packaging laminate are to be folded double.
There is thus still a need in the art for a simple and cost-efficient method of solving the above-described problem in connection with the conventional single-use packages.